Something used in only one proof is a trick. If it is used in two proofs it becomes a lemma. Calculus is used as a filter. It is not taught because you will ne

Something used in only one proof is a trick. If it is used in two proofs it becomes a lemma. Calculus is used as a filter. It is not taught because you will need it in the future, it is used to detect second rate minds. It is debatable whether this is an appropriate use .